Live mail screening is a technique which allows seeing through envelopes and small parcels, enabling the detection of suspicious items such as powders or electrical circuits prior to opening the mail and exposing these contents. It is known in the art of mail screening to use radiation in the long terahertz (THz) wavelengths, for example between 700 μm and 1075 μm, as the penetration depth of the THz radiation is long enough to see through envelopes and small parcels.
There remains a need in the field for a practical and efficient apparatus for screening mail or similar small objects.